In a crane, especially a telescoping-boom crane, at the boom point or head, the cable for lifting the load can extend downwardly to terminate at its lower end in a block or other unit of tackle engaging the load. A danger upon operation of such a crane is that the tackle will impact upon the crane head or point.
To prevent such impact, the head of the crane may be provided with a lift-limiting switch which, upon operation, will terminate the lifting operation.
In the telescoping crane system of U.S. Pat. No. 5,213,660, a weight is mounted on the cable and is suspended for a ligature which is connected to the lift-limiting switch at the head of the crane. While the weight applies tension to the ligature, lifting can proceed. When the lower load block, i.e. the load-engaging tackle, is lifted to raise the weight, the tension on the ligature is relaxed to allow the switch to automatically shift into a position which deactivates the winch and terminates the lifting operation.
Weight suspended from a boom in another system is found in U.S. Pat. No. 4,535,899 and reference may also be had, in this connection, to German Patent documents DE-OS 1,756,076 and DE-OS 28 46 394.
The weights for operating the lift-limiting switch may consist of a number of pieces in prior art systems but to apply the weight to the cable or remove the weight from the cable generally the weight must be disassembled, thereby complicating the operation and making the process time-consuming. Furthermore, the fact that the device must be disassembled permits parts to be lost.